Power supply apparatuses employ power semiconductor devices, such as diodes, transistors and IGBTs. The life of power semiconductor devices tends to be shorter as the difference between the temperature of the devices when they are operating and the temperature when they are not operating becomes larger. When a power supply apparatus is used with, for example, an arc welder, a cutter, or an electroplating apparatus, it may be subjected to alternation between activation and deactivation at relatively short intervals. Power semiconductor devices of such power supply apparatus are subjected to frequent temperature changes, which further reduces the lives of the semiconductor devices. JP 2000-166217 A proposes a technique for solving this problem,
According to JP 2000-166217A, when the power supply apparatus is activated by turning an activation switch on, a fan also starts to be driven to cool the power semiconductor devices to suppress rising of the temperature of the devices. When the activation switch of the power supply apparatus is turned off, the fan is stopped to suppress lowering of the temperature of the power semiconductor devices. This reduces the difference between the temperature of the power semiconductor devices when they are operating and the temperature when they are no operating.
The following problem occurs when the fan is stopped at the same time as the power supply apparatus activation switch is turned off. Specifically, the power semiconductor devices are mounted, in many cases, on a heat sink in the power supply apparatus. If the fan is stopped at the same time as the turning off of the power supply apparatus activation switch, heat will stay and stand in the vicinity of the heat sink, which gives thermal stress to components around the heat sink. To avoid it, the driving of the fan must be continued even after the power supply activating switch is turned off. This, however, causes the temperature of the power semiconductor devices to be lowered too much, and, therefore, the life of the power semiconductor devices cannot be maintained.
An object of the present invention is to provide a power supply apparatus with power semiconductor devices having a life maintained without giving thermal stress to components except for the power semiconductor devices of the power supply apparatus.